In recent years, a light-emitting element such as a light emitting diode is widely used as an illuminant for a lighting display board and a back light illuminant for a portable phone or a personal computer due to an improvement of a luminance thereof. Such a light-emitting element is used in the state that the light-emitting element is housed in a package for housing a light-emitting element.
Conventionally, for such a package for housing a light-emitting element, a cavity for housing a light-emitting element is formed on the upper face of an insulating substrate composed of one or a plurality of insulating layers laminated.
Moreover, a wiring pattern layer is formed in a bonded manner on an area from the bottom face to the outside of the cavity. The wiring pattern has a function for supplying to a light-emitting element a current that has been supplied from an external electric circuit, thereby generating a specified luminance. After the light-emitting element is mounted on the bottom face of the cavity through a bump electrode in such a manner that each electrode of the light-emitting element is electrically connected to the wiring pattern layer, the light-emitting element is air-tightly sealed in the cavity by filling with a glass or a transparent resin such as an epoxy resin, thereby fabricating a light-emitting apparatus as a final product.
For the package for housing a light-emitting element, there is bonded a light reflecting layer for reflecting a light emitted from the light-emitting element to an inside wall of the cavity of the insulating substrate so as to substantially increase a luminance of the light-emitting element. The light reflecting layer causes a light emitted from the light-emitting element to be bright and the characters and images that are displayed as a lighting display board to be bright and extremely vivid.
As the light reflecting layer, gold, silver, nickel, aluminum, rhodium, platinum or the like is suitably used. For instance, a metallization metal layer is bonded to the inside wall of the cavity of the insulating substrate in advance, and gold, silver, nickel, aluminum, rhodium, platinum or the like is bonded to the metallization metal layer by a plating method, a vacuum deposition, a sputtering method or the like, thereby forming the light reflecting layer in a bonded manner on the inside wall of the cavity of the insulating substrate. The light reflecting layer is not formed on the entire inside wall of the cavity, but is formed in a bonded manner at a distance from the bottom face of the cavity, thereby effectively preventing an electrically short circuit between the light reflecting layer and a wiring pattern layer on the bottom face of the cavity.
As a conducting method to a light-emitting element for such a package for housing a light-emitting element, there is proposed for instance a conducting method disclosed in Patent document 1 (Japanese Laid-Open Patent Publication No. 2002-232017). More specifically, as shown in FIG. 4, a package 100 for housing a light-emitting element related to Patent document 1 is provided with an insulating substrate 111 and a reflector frame 112 disposed on the peripheral section of the insulating substrate 111, and a cavity 119 for housing a light-emitting element is formed between the insulating substrate 111 and the reflector frame 112.
A through hole for wiring (so-called via hole) 116 provided so as to vertically pass through the insulating substrate 111 is formed in such a manner that it is positioned at the cavity 119 for housing a light-emitting element of the insulating substrate 111, that is, under the cavity 119 for housing a light-emitting element. A conductive material 117 is filled in the through hole for wiring 116, and wiring pattern layers 114 and 115 on the upper and bottom faces of the insulating substrate 111 conduct to each other through the conductive material 117. Consequently, a light-emitting element 118 mounted on the wiring pattern layer 114 on the upper face can electrically conduct to an external electric circuit.
Moreover, as a conducting method to a light-emitting element, for a package 200 for housing a light-emitting element disclosed in Patent document 2 (Japanese Laid-Open Patent Publication No. 1996-274378), as shown in FIG. 5, a through hole for wiring 216 is formed from the bottom of the cavity 219 for housing a light-emitting element of the insulating substrate 212 through an intermediate wiring portion 213 formed at the intermediate position of the insulating substrate 212 to the bottom face of the insulating substrate 212. A conductive material 217 is filled in the through hole for wiring 216, and wiring pattern layers 214 and 215 on the upper and bottom faces of the insulating substrate 212 conduct to each other through the conductive material 217. Consequently, a light-emitting element 218 mounted on the wiring pattern layer 214 on the upper face can electrically conduct to an external electric circuit.
Furthermore, for a package for housing a light-emitting element 300 disclosed in Patent document 3 (Japanese Laid-Open Patent Publication No. 2003-37298) and Patent document 4 (Japanese Laid-Open Patent Publication No. 2003-273405), as shown in FIG. 6, a through hole for wiring is not formed in the insulating substrate 311, and a wiring pattern layer 301 disposed between a reflector frame 312 and the insulating substrate 311 is arranged on the outside face of the insulating substrate 311 in such a manner that wiring pattern layers 314 and 315 formed on the upper and bottom faces of the insulating substrate 311 conduct to each other through the wiring pattern layer 301. Consequently, a light-emitting element 318 mounted on the wiring pattern layer 314 on the upper face can electrically conduct to an external electric circuit.
As described above, there are some methods to conduct to a light-emitting element, and a light-emitting element is mounted in a package for housing a light-emitting element in such a manner that the light-emitting element can electrically conduct to an external electric circuit by the methods.
[Patent document 1] Japanese Laid-Open Patent Publication No. 2002-232017
[Patent document 2] Japanese Laid-Open Patent Publication No. 1996-274378
[Patent document 3] Japanese Laid-Open Patent Publication No. 2003-37298
[Patent document 4] Japanese Laid-Open Patent Publication No. 2003-273405
As described above, for the conventional packages for housing a light-emitting element disclosed in Patent documents 1 and 2, and further depicted in FIGS. 4 and 5, the through holes for wiring (so-called via holes) 116 and 216 are formed directly below the cavities 119 and 219 for housing a light-emitting element so as to vertically pass through the insulating substrates 111 and 211.
In the case in which the insulating substrate is made of ceramics, the via hole and a wiring pattern that is electrically connected to the via hole are formed in general by filling a conductive paste mainly composed of a high melting point metal such as tungsten in a through hole formed in a green sheet by a method such as punching, by carrying out a screen printing of a conductive paste in such a manner that the exposed face of the filled portion is covered in order to form a pattern at the specified position, and by carrying out degreasing and sintering (burning).
In the case in which wiring a wiring pattern is formed on the via hole by such a method, it cannot be avoided that a peripheral section of the through hole is deformed in punching (a peripheral section is protruded or depressed depending on a direction of punching) and a high melting point metal section filled in the through holes for wiring 116 and 216 and the peripheral section thereof are protruded since a contraction behavior in sintering for the high melting point metal filled in the through hole is different from that for ceramics. As a result, the wiring pattern layers 114 and 214 that have been bonded onto the insulating substrate are not flat. It is difficult in practice that the above protrusion is suppressed by not sufficiently filling a high melting point metal into the through hole to form a flat pattern. That is because, in the case in which a filled amount is decreased, a cavity is formed on the contrary or a crack or a blow hole is generated in a conductive layer in the through hole since a contraction of the high melting point metal in burning is large, thereby causing an electrical connection failure or an increase in a conductivity.
Consequently, in the case in which a light-emitting element is mounted such protruded wiring pattern layers 114 and 214 through a bump electrode, a part of the light-emitting element is shifted or detached, or a disconnection or a conductive failure occurs in some cases, thereby preventing a part of a head light or a lighting fixture in which the light-emitting element has been installed from being lighted.
Moreover, in the case in which a wiring pattern layer 301 is arranged on the outside face of the insulating substrate 311 as disclosed in Patent document 3, and depicted in FIG. 6, a wiring distance from the wiring pattern layer 315 formed on the bottom face of the insulating substrate 311 through the wiring pattern layer 301 formed on the outside face and the wiring pattern layer 314 formed on the upper face to the light-emitting element 318 is larger depending on a size of the insulating substrate 311, thereby causing a failure such as a short circuit or a disconnection.
Moreover, since the wiring pattern layer 301 is arranged on the outside surface of the substrate, the wiring is concentrated on one section and a complicated wiring pattern layer must be used in some cases. Furthermore, the complicated wiring pattern layer causes a time taken for a circuit design to be longer and a development cost to be higher.
In addition, in the case in which the wiring pattern layer 301 is arranged on the outside surface of the substrate, the layer becomes thin due to a restriction of the fabrication method. More specifically, a substrate provided with a wiring pattern layer to be arranged on the outside surface is fabricated in general by forming a through hole in the substrate (or a green sheet that is a precursor thereof), coating a paste containing a high melting point metal with a thickness of approximately 15 μm on the inside wall of the through hole, sintering the metal paste by a cofire method, carrying out plating, and cutting the substrate along the face close to the center of the through hole as a cross section (in this case, two substrates can be obtained by one cutting). Consequently, since the wiring pattern layer 301 is comparatively thin to be approximately 20 μm even in the case in which a thickness of a plate is added, an electrical resistance is larger and a large current cannot be flown to the light-emitting element 118, thereby decreasing a luminance. Since it is preferable to form an exposed face by a plating layer, plating is carried out in advance in the above fabrication method in such a manner that a plating layer is exposed in cutting the through hole from the aspect of an efficiency.
The present invention was made in consideration of such conditions, and an object of the present invention is to provide a package for housing a light-emitting element in which a part of the light-emitting element is not shifted or detached, no disconnection or no conductive failure occurs, the light-emitting element can be reliably connected to the wiring pattern layer for connecting a light-emitting element, and it can be prevented that a part of a head light or a lighting fixture in which the light-emitting element has been installed is not lighted in the case in which the light-emitting element is mounted, and to provide a method for effectively manufacturing the package for housing a light-emitting element.
Moreover, another object of the present invention is to provide a package for housing a light-emitting element that is provided with a wiring pattern layer, capable of conducting to the light-emitting element without using a complicated wiring pattern layer, and to provide a method for manufacturing the package for housing a light-emitting element.
Furthermore, another object of the present invention is to provide a method for manufacturing the package for housing a light-emitting element, capable of simplifying a circuit design of the wiring pattern layer, lowering a development cost, and manufacturing the wiring pattern layer at a low cost.
Furthermore, another object of the present invention is to provide a package for housing a light-emitting element, capable of flowing a large current to the light-emitting element, thereby improving a luminance, and to provide a method for manufacturing the package for housing a light-emitting element.